Hi,
We can only answer HMRC queries on this forum so as regards the validity of stamping a passort please contact the Home Office.
If your uncle is importing the vehicle in to the UK then this will attract a VAT charge of 20%.
There may also be customs duties payable on the vehicle arriving in the UK. We would recommend speaking to our International Trade Team regarding any duties which may be payable.
Imports and exports: general enquiries
Thank you.